cords.  Cfo'Pty   WC*7 ,        /T) 

y 

.    .   Far: .ere'  ~~in  794. 

Feb.    1917. 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


CITRUS-FRUIT  IMPROVEMENT 

**- 

HOW  TO  SECURE  AND  USE  TREE- 
PERFORMANCE  RECORDS 

A.  D.  §HAMEL 

Physiologist  in  Charge  of  Fruit-Improvement  Investigations,  Office 
of  Horticultural  and  Pomological  Investigations 


FARMERS'  BULLETIN  794 
UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 


Contribution  from  the  Bureau  of  Plant  Industry 
WM.  A.  TAYLOR,  Chief 


Washington,  D.  C.   , 


,    February,  1917 


UN  OF  SUbfROntAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 


MANY  California  citrus  growers  have  reported  in 
recent  years  that  they  were  securing  lower  yields 
of  fruit  per  acre  than  in  the  earlier  history  of  their 
industry.  Complaint  also  has  been  made  that  an  in- 
creasing proportion  of  the  fruit  of  the  leading  com- 
mercial varieties  of  oranges  and  lemons  was  abnormal 
or  "  off  type "  in  size,  form,  color,  smoothness  of  skin, 
or  other  important  characteristics. 

Systematic  and  continued  investigation  of  this  subject 
in  the  groves  in  California  since  1909  has  disclosed  that 
a  considerable  proportion  of  the  deterioration  observed 
is  traceable  to  unintentional  propagation  of  undesir- 
able strains  of  the  leading  varieties  resulting  from  bud 
variation. 

The  results  obtained  in  bud-selection  experiments 
carried  on  during  the  past  five  years  indicate  that  by 
top-working  with  buds  from  those  having  consistently 
good  records  for  productiveness  and  quality  the  in- 
ferior or  "  drone "  trees  of  such  varieties  as  Washing- 
ton Navel  and  Valencia  oranges  can  be  made  productive 
and  profitable. 

This  bulletin  describes  the  methods  that  have  been 
found  effective  and  practicable  in  locating  the  desirable 
and  undesirable  trees  in  groves  and  for  transforming 
the  latter  when  found. 


c 


CITRUS-FRUIT  IMPROVEMENT:  HOW  TO  SECURE 
AND  USE  TREE-PERFORMANCE  RECORDS. 


CONTENTS. 


Page. 

Introduction 3 

Bud  variation 4 

The  object  of  performance  records 5 

Methods  of  securing  the  records 5 

Tree  numbers 5 


Picking 

Weighing 

Recording  the  results. 


Page. 

The  uses  of  performance  records 12 

Bud-wood  selection 12 

Top-working  undesirable  trees 12 

Care  of  bud  wood 14 

Budding 14 

Summary 15 


INTRODUCTION. 

The  established  and  proved  citrus  varieties  are  the  most  valuable 
possession  of  the  citrus  industry.  The  conservation,  standardization, 
and  stabilization  of  these  varieties  should  receive  most  careful  con- 
sideration by  citrus  propagators  and  growers. 

The  deterioration  or  "  running  out "  of  these  varieties .  through 
the  unintentional  propagation  of  undesirable  strains  is  responsible 
for  a  large  proportion  of  the  low  yields  of  inferior  fruits  in  many 
citrus  orchards.  The  introduction  of  new  varieties  to  take  the  place 
of  those  which  have  become  unprofitable  by  reason  of  the  use  of 
careless~  methods  of  propagation  is  usually  a  matter  of  experiment. 
The  establishment  of  new  varieties  requires  long  periods  of  time  to 
prove  their  value  to  the  grower  and  to  introduce  them  in  the  markets. 

The  use  of  individual-tree  records  of  production  in  citrus  orchards 
was  originally  introduced  into  California  by  the  writer  in  1909. 
The  utility  of  such  records  as  a  factor  in  the  practical  work  of 
standardizing  the  quality  and  quantity  of  fruit  production  in  estab- 
lished orchards  has  been  proved  experimentally  and  tested  com- 
mercially. As  a  result  of  these  investigations  thousands  of  nursery 
trees  have  been  propagated  and  inferior  trees  in  established  orchards 
top-worked  with  buds  selected  from  productive  trees  of  desirable 
strains  on  the  basis  of  their  performance  records  for  a  series  of 
years.  Several  thousand  of  these  trees  have  come  into  bearing,  and 
as  far  as  can  be  determined  from  trees  of  their  age  they  have  without 
exception  reproduced  the  strain  which  was  propagated. 

73214° — Bull.  794 — 17  3 


209937 


4  FARMERS'  BULLETIN  794. 

The  data  secured  during  a  6-year  investigation  of  the  nature 
and  amount  of  bud  variability  occurring  in  Washington  Navel 
orange  trees  in  California  will  be  presented  and  interpreted  in  an- 
other publication  of  the  United  States  Department  of  Agriculture. 
The  methods  of  commercial  orchard  practice  recommended  here  are 
based  on  the  results  of  that  investigation. 

The  importance  of  individual-tree  performance  records  as  a  basis 
for  measuring  the  effects  of  cultural  or  other  tree  treatments,  both  in 
investigational  and  commercial  work,  has  become  so  evident  that 
such  records  are  now  regarded  by  the  most  efficient  and  successful 
California  citrus  growers  as  of  great  value  in  all  orchard  work. 
When  making  changes  in  methods  of  tree  culture  or  care,  the  way  to 
determine  definitely  whether  such  changes  are  of  value  is  to  secure 
performance  records  of  the  trees  both  before  and  after  the  new  sys- 
tems are  put  into  practice.  The  increasing  demand  from  growers 
for  advice  regarding  a  practical  method  of  keeping  individual  citrus- 
tree  performance  records  has  made  necessary  the  publication  of  this 
bulletin. 

BUD  VARIATION. 

Although  there  is  no  generally  accepted  theory  to  account  for  bud 
variability  in  citrus  trees,  bud  variation  is  of  more  or  less  frequent 
occurrence  in  trees  of  all  varieties.  It  may  manifest  itself  in  the 
habit  of  growth  of  the  trees  or  their  method  of  branching,  the  size, 
form,  texture,  or  color  of  the  foliage,  or  the  form,  color,  texture, 
abundance,  or  scarcity  of  the  fruits.  Occasionally  one  tree  grown 
from  a  single  bud  will  develop  several  distinct  strains  of  fruit. 
Frequently  a  single  fruit  or  a  branch  bearing  several  fruits  will  be 
found  on  a  tree  having  characteristics  distinct  from  the  fruits  of  the 
typical  strain  borne  by  the  tree  as  a  whole.  Minor  variations  in 
fruit  characteristics  are  of  very  frequent  occurrence. 

Individual-tree  performance  records  reveal  the  extent  to  which 
trees  in  commercial  plantations  differ  from  one  another  in  their  regu- 
larity of  hearing  and  in  the  quality,  quantity,  and  character  of  the 
fruit  produced. 

The  nursery  propagation  of  bud  variations  may  be  largely  avoided 
through  the  use  of  buds  selected  from  individual  trees  the  per- 
formance records  of  which  have  shown  them  to  be  heavy  annual 
producers  of  fruit  of  a  desirable  strain.  Healthy  citrus  trees  of 
inferior  strains  in  established  orchards  may  be  successfully  top- 
worked  to  the  best  strain  and  may  thus  convert  into  an  asset  what 
was  formerly  a  liability  of  the  orchard. 


CITRUS-FRUIT  IMPROVEMENT.  ^  5 

THE  OBJECT  OF  PERFORMANCE  RECORDS. 

The  object  of  securing  individual  citrus-tree  performance  records 
is  to  obtain  reliable  information  as  to  the  behavior  of  individual 
trees  in  established  bearing  orchards.  This  information  may  be 
utilized  in  the  elimination  of  inferior  or  drone  trees  by  top-working 
or  removing  them,  in  the  selection  and 'location  of  particularly 
good  trees  for  use  as  sources  of  bud  wood  for  propagation,  in  study- 
ing the  results  of  individual  tree  treatments,  and  for  other  pur- 
poses wrhere  it-  is  important  to  know  definitely  the  amount  and 
value  of  fruit  production.  Individual-tree  performance  records 
enable  citrus  growers  to  replace  indefinite  and  oftentimes  unre- 
liable opinions  as  to  orchard  conditions  by  exact  and  definite  infor- 
mation, from  which  safe  conclusions  may  be  drawn. 

METHODS  OF  SECURING  THE  RECORDS. 

TREE  NUMBERS. 

The  first  step  in  securing  individual-tree  performance  records 
is  to  number  each  tree,  so  that  the  record  of  the  trees  may  be  kept 
during  successive  years  without  danger  of  confusion  and  mistakes 
in  securing  and  entering  the  performance-record  data  and  other 
notes. 

The  numbering  system  evolved  in  the  investigation  of  this  prob- 
lem has  been  adopted  by  many  citrus  growers.  It  provides  for 
giving  each  tree  a  number  consisting  of  three  sets  of  figures.  This 
individual  tree  number  is  made  up  of  the  number  of  the  block  or 
division  of  the  orchard,  the  number  of  the  row  in  which  the  tree 
occurs,  and  the  position  of  the  tree  in  the  row,  counting  always 
from  some  fixed  point,  such  as  the  irrigation  head;  for  instance,  a 
tree  located  in  block  2,  row  4,  and  the  tenth  tree  in  the  row  will 
have  the  number  2-4-10. 

The  numbers  can  usually  be  painted  on  the  tree  trunk  or  on  one 
of  the  main  limbs.  It  has  been  found  most  convenient  to  place 
these  numbers  in  a  vertical  column,  and  they  are  more  easily  read 
when  arranged  in  this  form.  Pure  white-lead  paint  and  an  ordi- 
nary lettering  brush  should  be  used  for  this  work.  The  numbers 
should  always  be  placed  in  the  same  relative  position  on  all  of  the 
trees  in  an  orchard,  so  that  they  may  be  easily  found  at  any  time. 
Where  it  is  not  possible  to  paint  the  number  on  the  tree  it  can  be 
painted  or  stamped  on  a  wooden  or  metal  tag,  which  should  be 
attached  to  the  tree  where  it  can  be  easily  seen  and  in  such  a  manner 
as  not  to  interfere  with  the  future  growth  of  the  tree.  Large  plain 
figures  should  be  used,  so  that  the  number  can  be  read  from  some 
distance.  One  man  can  usually  number  175  or  more  trees  in  a  day. 


6  FARMERS'  BULLETIN  794. 

This  system  will  prevent  the  duplication  of  numbers,  no  matter 
how  many  blocks  or  trees  there  are  in  the  orchard ;  it  will  locate  any 
particular  tree,  so  that  it  can  be  easily  found  at  any  time  for  indi- 
vidual-tree care,  for  the  consideration  of  its  performance  record, 
or  for  other  purposes;  and  it  will  promote  accuracy  and  simplicity 
in  recording  individual-tree  data. 

It  seems  advisable,  in  order  to  secure  uniformity  and  accuracy  in 
tree  numbers,  to  advise  the  members  of  associations  of  fruit  growers 
to  have  the  numbers  painted  on  the  trees  by  a  regular  crew  managed 
by  the  association,  as  is  the  practice  at  the  present  time  in  picking 
the  crops.  It  can  doubtless  be,  arranged  by  most  associations  to  have 
some  members  of  the  regular  picking  crew  attend  to  the  tree-number 
work  before  the  regular  picking  season  begins  or  during  a  slack 
period  in  that  season. 

PICKING. 

The  organization  of  the  picking  crew  should  be  such  that  one 
man  picks  the  fruits  of  an  individual  tree.  The  crew  can  usually  be 
organized  so  that  each  picker  is  assigned  to  a  row  of  trees.  This 
arrangement  frequently  induces  some  rivalry  among  the  pickers 
and  will  usually  result  in  more  rapid  and  efficient  work  than  has 
heretofore  been  the  case.  Where  tree  records  are  not  kept,  two  or 
more  pickers  as  a  rule  work  on  the  same  tree,  but  this  practice  is  not 
desirable  where  performance  records  are  to  be  secured. 

The  picking  boxes  should  be  distributed  to  the  individual  trees 
instead  of  being  assembled  in  box  rows.  A  little  practice  wTill  enable 
the  distributors  of  the  boxes  to  determine  about  the  number  of  boxes 
required  to  hold  the  crop  of  each  tree. 

The  picker  should  always  empty  his  picking  sack  after  finishing 
each  tree,  so  as  to  avoid  carrying  any  fruits  to  the  next  tree.  The 
boxes,  after  being  filled,  should  be  assembled  in  the  shade  of  the  tree 
from  which  the  fruits  were  picked  in  order  to  protect  them  from  the 
sun. 

WEIGHING. 

The  crop  of  fruit  of  each  pick  from  an  orange  or  grapefruit  tree 
can  be  expressed  in  terms  showing  the  number  of  full  and  partly 
filled  boxes  borne  by  the  tree.  In  the  case  of  lemon  or  lime  trees, 
where  frequent  picks  are  usually  made  from  each  tree,  the  amount 
of  each  pick  can  be  expressed  in  a  manner  similar  to  that  for  orange 
and  grapefruit  trees  or,  as  is  usually  done,  by  determining  the  actual 
weight  of  the  fruits  and  recording  the  results  in  terms  of  pounds. 

Many  citrus  growers  who  are  keeping  individual-tree  records  in 
their  orchards  have  found  that  a  record  of  the  number  of  full  boxes 
and  the  estimated  amount  of  fruit  in  the  partly  filled  boxes  is  suffi- 


CITRUS-FRUIT   IMPROVEMENT  7 

ciently  accurate  for  their  purposes.  This  method  does  away  with 
the  necessity  for  any  apparatus  for  weighing  the  fruits.  Where  a 
considerable  proportion  of  the  crop  of  full-bearing  trees  is  picked  at 
one  time  this  method  of  recording  the  amount  of  the  yield  of  the 
individual  trees  will  doubtless  prove  to  be  satisfactory.  Where  the 
amount  of  the  pick  from  the  trees  is  small,  a  more  accurate  record 
will  be  obtained  by  weighing  the  fruits. 

A  convenient  method  for  determining  the  amount  or  weight  of  the 
fruit  in  the  picking  boxes  is  shown  in  figure  1.  Figure  2  shows  (at  A ) 
a  shoulder  harness,  by  means  of  which  an  inexpensive  spring  balance, 
Z?,  is  carried.  The  scale,  #,  provides  for  weighing  a  maximum  of 


FIG.  1. — Weighing  citrus  fruits 


P923A-HP 

>xes  for  individual-tree  performance  records. 


50  pounds.  The  opposite  scale,  Z>,  is  calibrated  by  actual  trials 
of  empty  and  full  picking  boxes,  the  box  tare  being  marked  as 
0  and  the  weight  of  a  full  box  as  10.  The  space  between  these 
marks  is  divided  into  10  equal  parts,  numbered  from  1  to  10.  Such 
an  arrangement  provides  for  determining  the  amount  of  the  crop  in 
the  partly  filled  box  either  in  terms  of  pounds  or  as  tenth  parts  of 
boxes,  as  desired. 

The  ropes,  d,  are  provided  with  steel  hooks,  e,  so  that  they  can  be 
easily  attached  to  the  ends  of  the  picking  boxes.  In  using  these 
scales  the  weigher  attaches  the  hooks  to  the  ends  of  the  box,  rises, 
assuming  an  upright  position,  thus  lifting  the  box  from  the  ground, 
and,  with  the  box  swinging  free,  reads  the  weight  of  the  fruit. 


8 


FARMERS'  BULLETIN  794. 


A  little  experience  with  this  balance  will  enable  the  weigher  to 
secure  accurate  records  of  the  amount  of  fruit  in  the  picking  boxes. 
In  the  case  of  a  picking  crew  of  25  to  50  men  the  Aveigher  will 
also  have  time  to  help  inspect  and  distribute  empty  picking  boxes, 

load  the  filled  boxes  on  the  or- 
chard wagons,  and  perform 
such  other  duties  as  may  be  nec- 
sary  to  insure  the  careful  han- 
dling of  the  boxes  of  fruit. 

It  has  been  found  by  expe- 
rience that  in  order  to  secure 
reliable  individual-tree  records 
it  is  desirable  to  have  one  of 
the  regular  picking  crew  attend 
to  this  matter.  In  one  large 
citrus  planting,  where  individ- 
ual-tree records  have  been  kept 
for  several  years  and  the  pick- 
ing is  done  by  crews  of  Mexi- 
can laborers,  one  Mexican  in 
each  crew  keeps  the  records,  in- 
spects the  empty  picking  boxes, 
and  does  such  other  work  as  is 
required  in  order  to  promote 
the  careful  handling  of  the 
fruits. 

In  other  cases  the  foremen  of 
the  picking  crews  are  expected 
to  keep  the  individual  tree  rec- 
ords in  addition  to  their  other 
duties.  This  plan  has  been 
found  to  be  less  successful  than 
where  an  extra  laborer  for  each 
picking  crew  is  provided  for 
this  purpose. 

In  association  picking  crews, 
where  the  crops  of  the  individ- 
ual members  of  the  association  are  picked  by  a  general  picking  crew, 
the  individual-tree  records  can  be  secured  in  the  smaller  orchards  by 
the  simple  expedient  of  adding  one  regular  laborer  to  each  picking 
crew.  Any  intelligent  person  can  quickly  learn  how  to  keep  the 
individual-tree  records  and  assist  in  handling  the  fruits,  so  that  the 
expense  of  the  extra  man  can  be  justified  from  this  standpoint. 


FIG.  2. — Details  of  the  weighing  apparatus 
shown  in  figure  1  :  A,  Shoulder  harness ; 
B,  spring  balance ;  a,  scale  for  weighing  a 
maximum  of  50  pounds  ;  b,  scale  calibrated 
to  indicate  full  box  or  parts  of  box  in 
tenths ;  c,  pointer ;  d,  d,  ropes ;  and  e,  e, 
steel  hooks. 


CITRUS-FRUIT   IMPROVEMENT.  9 

RECORDING  THE  RESULTS. 

The  date  of  picking  and  the  quantity  and  quality  of  the  product 
of  each  tree  should  be  recorded  so  that  it  can  be  easily  classified  and 
compiled  for  the  intelligent  consideration  of  that  individual  tree's 
behavior.  The  three  forms  shown  herewith  are  suggested  for  the  use 
of  those  who  wish  to  keep  such  records.  The  successful  use  of  similar 
forms  in  commercial  performance-record  keeping  has  proved  their 
practicability.  Experience  with  these  forms  has  shown  that  a  sheet 
of  convenient  size  is  one  which  provides  space  for  recording  the 
yields  of  40  trees.  These  sheets  should  have  a  stiff-back  loose-leaf 
cover  or  be  perforated  and  bound  in  covers  to  facilitate  their  use  in 
the  orchard  and  to  make  it  possible  to  assemble  the  records  of  any 
particular  block. 

The  form  recommended  for  keeping  orange  and  grapefruit  indi- 
vidual-tree performance-record  data  for  a  maximum  of  four  picks 
in  one  season  from  each  tree  is  shown  in  Table  I,  A. 

The  form  recommended  for  use  in  keeping  individual  lemon  and 
lime  tree  performance-record  data,  providing  for  a  maximum  of  1'2 
picks  each  season,  is  shown  in  Table  I,  B.  In  this  form  provision  is 
made  for  recording  the  quantity  of  fruit,  either  in  terms  of  pounds 
or  as  the  number  of  full  and  partly  filled  boxes,  for  a  maximum  of 
12  picks  from  each  tree  during  the  season. 

The  commercial  grade  of  the  fruits  of  the  individual  trees  can  be 
recorded  by  the  use  of  the  following  or  a  similar  system:  A  may  be 
used  to  designate  the  best  or  first-grade  fruits;  Z?,  inferior,  blemished, 
or  second-grade  fruits;  6",  cull  or  third-grade  fruits;  and  $,  extremely 
variable  fruits  as  regards  shape,  size,  color,  or  other  characteristics. 
This  system  can  be  extended,  if  desired,  to  cover  other  matters  of 
importance  in  individual-tree  care,  as,  for  instance,  the  letter  X,  to 
call  attention  to  particularly  good  trees  which  may  be  found  suitable 
for  the  selection  of  bud  wood  for  propagation ;  Z>,  to  suggest  diseased 
or  injured  trees ;  F,  to  mark  such  trees  as  may  need  fumigation ;  F,  to 
show  the  need  of  pruning;  T,  to  indicate  an  undesirable  tree  which 
should  be  top-worked  or  removed;  and  such  other  letters  or  symbols 
can  be  employed  as  may  be  of  value  in  systematic  individual-tree  care. 


DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


10 


FARMERS*   BULLETIN   794. 


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12  FARMERS'   BULLETIN   794. 

The  data  showing  the  total  yield  of  each  tree  and  the  related  notes 
should  be  transferred  to  a  period  citrus-tree  record  form,  such  as  is 
shown  in  Table  I,  C.  This  form  provides  for  bringing  together  the 
records  of  several  successive  seasons,  so  that  the  behavior  of  each  tree 
during  a  given  period  may  be  studied  and  compared  with  that  of 
other  trees  grown  under  similar  conditions.  The  number  of  seasons' 
records  necessary  for  this  purpose  varies  somewhat  according  to  the 
conditions,  but  in  all  cases  an  even  number  of  seasons'  records  is  de- 
sirable. As  a  rule,  the  records  of  full-bearing  trees  for  two  successive 
normal  seasons  have  been  found  to  be  a  sufficient  basis  for  determin- 
ing the  relative  value  of  individual  citrus  trees  for  commercial  fruit 
growing.  The  records  of  four  successive  normal  seasons  will  prob- 
ably be  adequate  for  use  as  a  basis  for  the  selection  of  parent  trees  as 
sources  of  bud  wood  for  propagation.  In  any  event  two  years'  ex- 
perience will  demonstrate  to  every  grower  the  importance  of  indi- 
vidual-tree records,  from  which  he  can  easily  draw  his  own  con- 
clusion as  to  length  of  the  period  he  should  keep  these  records.  So 
far  in  the  cooperative  work  of  this  character  not  a  single  grower  has 
dropped  the  individual-tree  record  work  after  having  started  it,  and 
some  of  the  records  now  cover  a  period  of  six  years. 

THE  USES  OF  PERFORMANCE  RECORDS. 

BUD-WOOD   SELECTION. 

Citrus  bud  wood  for  commercial  propagation  should  be  cut  only 
from  the  best  trees  of  the  most  valuable  strain.  These  trees  should 
be  selected  on  the  basis  of  their  performance  records  and  from 
intimate  individual-tree  knowledge. 

Only  fruit-bearing  bud  wood  should  be  used  for  propagation. 
Every  bud  stick  should  have  one  or  more  typical  fruits  attached, 
if  possible,  when  cut  from  the  select  parent  trees,  as  shown  in  figure 
3.  By  the  use  of  this  method  more  buds  can  be  secured  from  pro- 
ductive and  desirable  trees  than  from  unproductive  and  undesirable 
ones.  Such  bud  wood  has  been  found  to  produce  trees  of  satis- 
factory growth,  as  well  as  early  and  regular  yields  of  fruit. 

In  the  past,  sucker  growth  has  been  generally  used  for  propaga- 
tion, and  little  or  no  attention  has  been  paid  to  the  number  or 
quality  of  the  fruits  borne  by  the  trees  from  which  bud  wood  has 
been  secured.  This  practice  has  naturally  led  in  many  cases  to  the 
propagation  of  inferior  strains.  The  large  proportion  of  trees  of 
undesirable  strains  in  many  citrus  orchards  is  due  to  this  lack  of 
care  in  the  selection  of  bud  wood. 

TOP-WORKING  UNDESIRABLE   TREES. 

The  elimination  from  established  orchards  of  trees  of  undesirable 
strains  has  been  effected  by  top-working  these  trees  with  select  buds 
from  trees  of  a  desirable  strain. 


CITRUS-FRUIT  IMPROVEMENT. 


13 


While  trees  of  some  of  the  inferior  strains  can  be  recognized  from 
their  habit  of  growth  or  other  vegetative  characteristics,  it  is  de- 
sirable wherever  possible  to  make  the  final  selection  of  trees  to  be 
top-worked  on  the  basis  of  their  performance  records  and  the  char- 
acteristics of  the  fruits  borne  by  them. 

The  selection  of  the  bud  wood  for  top-working  purposes  was  based 
on  individual-tree  performance  records  and  an  intimate  knowledge 
of  tree  characteristics  secured  by  careful  observation. 

The  first  top-working  on  a  commercial  scale,  as  a  result  of  the 
bud-selection  investigations  of  the  Department  of  Agriculture,  was 
done  in  the  summer  of  1911.  In  a  235-acre  orchard  of  8-year-old 
Eureka  lemon  trees,  approximately  2.500  trees  of  inferior  strains 


FIG.  3. — Typical  fruit-bearing  citrus  bud  wood  recommended  for  use  in  propagation. 

were   top-worked   with   buds   from   carefully   selected   trees   in  the 
same  orchard. 

Notwithstanding  the  extremely  cold  weather  of  the  succeeding  two 
winters,  which  very  seriously  injured  the  growth  from  these  buds, 
the  rebudded  trees  are  at  the -present  time  as  productive  as  the  other 
trees  in  the  orchard,  and  without  exception  the  strain  which  wTas 
propagated  has  been  reproduced,  as  far  as  can  be  determined  from 
trees  of  their  age.  Each  year  since  that  time  several  thousand 
trees  in  various  citrus  orchards  in  California  have  been  budded  or 
top-worked  on  the  same  basis,  and  those  which  have  reached  bearing 
age  have  reproduced  the  characteristics  of  the  strain  which  was 
propagated. 


14  FARMERS'  BULLETIN  7U4. 

CARE  OF  BUD  WOOD. 

Citrus  bud  wood  should  be  used  as  soon  as  possible  after  it  is  cut 
from  the  select  parent  trees.  If  it  is  necessary  to  keep  the  bud  wood 
for  some  time  before  it  is  used,  it  should  be  packed  in  moist,  steri- 
lized sphagnum  moss  and  stored  in  a  cool  room  having  fairly  uni- 
form conditions  of  temperature  and  humidity.  The  ideal  conditions 
for  such  a  room  are  a  temperature  of  about  70°  F.  and  a  relative 
humidity  of  80  to  90  per  cent.  The  moss  used  for  packing  the 
bud  wood  should  be  thoroughly  moistened  and  sterilized  with  live 
steam  for  about  an  hour,  after  which  it  can  be  run  through  an  ordi- 
nary clothes  wringer  in  order  to  squeeze  out  all  of  the  excess  mois- 
ture. Under  proper  storage  conditions  citrus  bud  wood  can  be 
kept  in  good  viable  condition  for  several  months. 

BUDDING. 

The  most  favorable  time  for  budding  is  generally  during  the 
spring  months.  However,  budding  can  be  done  successfully  at  any 
time  during  the  growing  period  of  the  trees.  With  some  varieties 
budding  in  the  late  fall  is  preferable  to  summer  budding,  as  the 
buds  will  remain  dormant  in  the  stocks  until  the  following  spring 
and  the  young,  tender  growth  of  the  buds  will  not  be  subjected  to 
the  extreme  climatic  conditions  of  the  winter  months.  High  bud- 
ding— that  is,  the  insertion  of  the  buds  as  high  on  the  stocks  as 
possible — is  recommended  for  California  conditions. 

In  top- working  undesirable  trees,  two  or  more  of  the  main  limbs 
should  be  selected  as  the  foundation  for  the  new  head,  as  shown  in 
figure  4.  The  select  buds  should  be  inserted  in  these  limbs,  two  or 
more  in  each,  about  1  to  2  feet  from  the  trunk  of  the  tree.  After 
the  buds  have  made  a  union  with  the  tree,  the  limbs  should  be  sawed 
off  about  6  inches  above  the  inserted  buds.  The  freshly  cut  surfaces 
should  be  covered  with  grafting  wax,  p.ure  lead  paint,  or  some 
pruning  compound,  and  the  remainder  of  the  tree  should  be  covered 
heavily  with  whitewash,  cloth,  or  other  material,  so  as  to  protect  the 
trunk  and  limbs  of  the  tree  from  sun  scald  or  other  injuries  due  to 
exposure.  After  about  a  year's  growth  the  limbs  should  be  cut  back 
again,  so  that  only  one  bud  is  left  on  each.  These  second  cuts  should 
slope  downward  from  a  point  directly  above  the  bud  union,  and  the 
surfaces  should  be  again  protected,  so  they  will  heal  completely. 

Top-worked  trees  should  be  inspected  frequently  for  the  first  two 
or  three  seasons  and  all  growth  removed  except  that  from  the  select 
buds.  In  one  or  two  years  the  growth  from  such  buds  will  begin 
bearing  fruits  and  should  reach  normal  production  in  from  three  to 
five  years,  depending  on  the  variety  and  the  climatic  and  cultural 
conditions. 


CITRUS-FRUIT   IMPROVEMENT. 
SUMMARY. 


15 


Bud  variation  in  citrus  fruits  is  of  more  or  less  frequent  occurrence 
and  of  great  economic  importance  to  citrus  growers. 

The  investigations  -now  under  way  indicate  that  undesirable  bud 
variations  can  largely  be  eliminated  from  commercial  citrus  planta- 
tions by  using  bud  wood  from  trees  known  to  continuously  produce 
fruit  of  the  character  desired.  The  determination  of  these  trees  is 


P62IA-HP 

FIG.  4. — A  Eureka  lemon  tree  of  an  unproductive  strain  10  years  old,  rebudded  to  a 
productive  strain,  showing  the  first  growth  of  the  buds  previous  to  the  final  cutting 
back  of  the  foundation  limbs. 

most  easily  and  satisfactorily  made  through  the  keeping  of  perform- 
ance records. 

Individual  citrus-tree  performance  records  are  being  kept  by  many 
citrus  growers. 

Records  for  an  even  number  of  successive  seasons  are  desirable. 
For  some  purposes  two  seasons'  records  of  full-bearing  trees  are 


IVtStON  OF  SUBTROPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 


probably  sufficient;  in  other  cases  lour  or  more  seasons'  records  ar' 
preferable.  The  longer  the  period  during  which  performance  rec 
ords  are  kept  and  the  greater  the  number  of  trees  recorded,  the  mor 
valuable  the  records  become. 

These  tree  records  enable  the  growers  to  locate  good  trees  froi 
which  bud  wood  may  be  secured,  poor  trees  to  be  top-worked 
select  buds,  and  trees  needing  individual  care.     They  also  providj 
reliable  data  on  which  to  base  conclusions  concerning  the  results  o\ 
tree  or  orchard  treatments. 

Each  tree  in  the  orchard  should  be  given  a  number,  by  means  o^ 
which  it  can  always  be  identified  and  easily  found. 

The  work  of  weighing  and  recording  the  crops  of  the  individual 
trees  can  be  done  with  little  extra  expense  by  adding  one  laborer  t( 
each  picking  crew.     This  cost  is  small  when  considered  in  connec 
tion   with  the  value  to   the   grower  of  the   information   obtain* 
thereby. 

Only  fruit-bearing  bud  wood  should  be  used  in  propagation, 
bud  wood  can  be  used  immediately  after  cutting,  or  it  can  be  kej 
in  moist,  .sterilized  moss  in  a  cool  room  for  several  months. 

The  spring  period  of  tree  growth  is  usually  the  best  time  for 
budding. 


L.US  ANGELAS 
LIBRARY 


-cf^s*r- 

.CM 


209937 


WASHINGTON  :  GOVERNMENT  PRINTING  OFF1CPI  :  1917 


his  book  is  J" ""  -n  the  last  date  star 


SB 
3*9 


A    001  095  392    5 


